OXYGEN POTENTIAL CONTROL IN YBA2CU3O7-DELTA THIN-FILMS

The oxygen potential of YBa2Cu3O7-delta (YBCO) films has been controlled by equilibrating the films with bulk YBCO in a quartz reaction system. The samples were heated up to 600-650-degrees-C and the oxygen content in bulk YBCO was controlled by evacuating a calculated amount of oxygen gas from the reaction system. The temperature was then gradually decreased to 400-degrees-C where the final equilibrium state was attained. The oxygen deficient films thus controlled have the same oxygen potential as the oxygen deficient bulk. The plots of c-axis lengths of the films against oxygen deficiency delta are almost parallel to those of the bulk in spite of having different c-axis lengths in the as-grown state. Thus the oxygen deficiency of as-grown YBCO films can be determined by comparing the c-axis length in the as-grown and fully oxygenated states. It is shown that YBCO as-grown films prepared under conventional deposition conditions are, in most cases, fully oxygenated except those cooled at lower oxygen partial pressure ( < 10(-2) Torr) after deposition. The T(c) versus delta relation of the oxygen deficient film with better as-grown superconducting transition showed a two-plateau behavior almost the same as that observed in the polycrystalline and single crystal samples with well defined delta.